A device for placing sheets on a stack is known from U.S. Pat. No. 5,518,230. There, on a rotating drivable sheet stack disk, which has two slits as sheet holders, arranged diametrically opposite one another, a sensor of a stack level sensor is coordinated with the rotating position of the sheet stack disk, mechanically controlled by an eccentric plate, in order to lift the sensor from the stack, automatically and mechanically controlled, for the release of stack, so as to place the next sheet on the stack. The sheet conveyor, known from the cited prior art, has two slits, diametrically opposed to one another, to accept the front edges of the sheets, so that already, the sheet conveyor is ready, in principle, once more, to take up the next sheet, while it places a preceding sheet.
In reality, this applies, however, only if the sheets to be taken over have a suitable format. A sheet is namely passed on to the conveyor, preferably by transport rollers on the end of a transport path for stock. A good placement of the sheet is attained, in particular, if the transport rollers release the back edge of the sheet just as the front edge of the sheet reaches a stop on a release site, because then the sheet is pliantly placed on a sheet stack. This means that the sheet should have a length with which it wraps around the sheet conveyor by just approximately half, that is, corresponding to approximately half the circumference of the jacket surface of the sheet conveyor. This is, by no means, always the case, however. Longer or shorter formats are also transported. Anyway, heavier and stiffer stock, for example, cannot be bent very much, free of damage, so that as a precaution with respect to such stock, the radius of the sheet conveyor is selected larger, rather, than would be suitable perhaps for the length of the sheet format. On the other hand, however, a uniform flow of sheets, if possible, should be transported for the utilization of the device, in which there will not arise an excessively large gap between successive sheets. However, successive sheets should not overlap either.
Thus, it may be that the free slit, which should carry out the next takeover, could be ready either too early or too late, depending on the situation. In view of the described situation, this problem would not be solved either by equipping the sheet conveyor with a larger number of slits (or with otherwise jaw-like holders).